The present invention relates to an apparatus and method for controlling the energization of a glow plug disposed in an internal combustion engine.
Hereinafter, the term “front” refers to a heating end side with respect to the axial direction of a glow plug, and the term “rear” refers to a side opposite the front side.
Glow plugs are generally equipped with resistance heaters and mounted on diesel engines to aid engine starting. Various energization control techniques have been proposed for the glow plugs.
Japanese Laid-Open Patent Publication No. 56-129763 and No. 60-67775 propose one type of glow plug energization control technique in which the energization control includes two control phases: “pre-glow” and “after-glow”. The pre-glow phase is performed upon actuation of a key switch to supply a large amount of power to the glow plug and raise the temperature of the resistance heater to a first target temperature rapidly during several seconds. The first target temperature is set at e.g. 1000° C. sufficiently high to assist engine starting at any time before the engine start. After the resistance heater reaches the first target temperature, the after-glow phase is performed to supply a smaller amount of power to the glow plug and maintain the temperature of the resistance heater at a second target temperature for a predetermined time period. The second target temperature is set at e.g. 900° C. so as to promote engine warm-up, prevent engine knocking and limit noise and white smoke developments and reduce HC emissions after the engine start.
In this energization control technique, however, the resistance heater temperature may once drop and become lower than the second target temperature immediately after shifting from the pre-glow phase to the after-glow phase or when the engine starts cranking during the after-glow phase.
In order to avoid such a drop in resistance heater temperature, Japanese Laid-Open Patent Publication No. 2004-232907 proposes another glow plug energization control technique in which the energization control includes four control phases: “pre-glow”, “upkeep glow”, “cranking glow” and “post-start glow (or after-starting glow)” in such a manner as to supply a larger amount of power to the glow plug during the cranking glow phase than during the preceding upkeep glow phase.